Whole blood may routinely be separated into its various components, such as red blood cells, platelets, and plasma. Conventional blood processing methods may use durable separator equipment (e.g., centrifuge, spinning membrane) in association with single use, sterile processing sets, typically made of plastic. The configuration of the single use processing sets used in combination with different separator equipment may vary widely, but some sets may include a molded plastic piece commonly referred to as a cassette. As used herein, the term “cassette” refers to a component of a blood processing system which includes a number of defined fluid passageways and valve stations. The cassette is commonly secured to a cassette holder of the durable equipment via motor-powered grippers or mechanical latches. The cassette holder may include actuators for opening and closing the valve stations, which determine which of the fluid passageways are connected to each other, thereby directing fluid between a number of sources and destinations.